1. Field of the Invention
The present invention relates to a protection circuit module for rechargeable batteries and a method of making the same.
2. Description of Related Art
A protection circuit module for rechargeable batteries prevents over-discharge from and overcharge to rechargeable batteries and is connected to the rechargeable batteries inside a battery pack for a mobile phone for example.
FIGS. 6 and 7a–7c show a conventional protection circuit module for rechargeable batteries. As shown in the figures, the protection circuit module, generally indicated by a reference numeral 61, comprises a substrate 62 in the form of a plate, a plurality of electronic components 63 mounted on the obverse surface of the substrate 62, and a resin sealer 64 sealing the electronic components 63. The substrate 62 is provided with a housing 65 enclosing the electronic components 63 and the resin sealer 64, and a conductor plate 66 is attached to each longitudinal end of the substrate 62.
The housing 65 includes a top wall 65a, a pair of lateral walls 65b extending longitudinally of the substrate 62 from the top wall 65a and a pair of end walls 65c extending widthwise of the substrate 62 from the top wall 65a. These walls define an enclosure for enclosing the resin sealer 64 and the electronic components 63. The resin sealer 64 provides waterproof effect to prevent the electronic components 63 from adversely affected by e.g. rain water coming into the battery pack of the mobile phone where the protection circuit module is incorporated. The resin sealer also protects the electronic components 63 from external force or damage.
As shown in FIGS. 7a–7c, the housing 65 has an outer surface provided with terminals 67 each including a contact portion 68a plated with gold, and the substrate 62 has a reverse surface provided with terminals 68 likewise plated with gold. These terminals 67, 68 are electrically connected to the electronic components 63, via a wiring pattern (not shown) formed on the obverse surface of the substrate 62, as well as a mobile phone body (not shown) or an external battery charger (not shown). The inner ends of the conductor plates 66 are electrically connected to the electronic components 63 via the wiring pattern (not shown) within the housing 65, whereas the outer ends projecting out of the substrate 62 are electrically connected to the rechargeable batteries (not shown) accommodated inside the battery pack (not shown).
The fabrication process of the protection circuit module 61 includes steps of mounting the electronic components 63 and the conductor plates 66 onto the substrate 62, applying the resin sealer 64 over the electronic components 63, and mounting the housing 65 onto the substrate 62. Among these three steps, the step of mounting the electronic components 63 and the conductor plates 66 as well as the step of mounting the housing 65 are both performed by reflow soldering, whereby if these two steps are performed at the same time, efficiency and productivity will improve.
However, the step of mounting the housing 65 onto the substrate 62 cannot be performed until the resin sealer 64 is applied over the electronic components 63. Therefore, these three steps must be taken one after another as long as the conventional structure shown in FIGS. 6 and 7a–7c is employed, whereby efficiency is difficult to improve.
Further, the resin sealer 64 is already applied when the housing 65 is bonded to the substrate 62 by reflow soldering, so that a heat-resistant thermosetting resin must be used for the resin sealer 64 to withstand high temperature of reflow soldering. A heat-resistant thermosetting resin, however, tends to contract when hardened, which may cause the substrate 62 to warp. Still further, a short circuit may occur between the electronic components 63 when the housing 65 is mounted to the substrate 62 by reflow soldering, because solder which serves as a bond between the substrate 62 and the electronic components 63 re-melts and expands. Still further, the screen printing method cannot be adopted for applying a solder paste to the substrate 62 after the electronic components 63 is mounted and the resin sealer 64 is applied, so that soldering for mounting the housing 65 must be performed manually, which also results in inefficiency